The Key? Compressed Air

We already know that a simple air duster can freeze padlocks, U-locks, and other types of locks to the point where you can shatter them with a hammer. But now you can use a can of compressed air to open security doors that are locked from the outside, not from the inside.

It's a whole lot easier, and far less destructive. Watch Samy's video to see the hack in action, then jump below for the explanation.

These types of access-controlled egress doors, typically seen in businesses where you need to be buzzed in or have an access code (PIN, card scan, etc.) to enter, have passive infrared (PIR) sensors on the inside so that people can freely exit without interference (for safety reasons... think fire).

As Samy notes, "The straw of these cans easily slips through most doors and allows you to aim the canister, while the output (technically not air, but typically a chemical such as difluoroethane) alters the temperature or amount of longwave infrared light that the sensor can detect, thus causing the sensor to believe there is motion, and unlocking the door from the outside."

It's an ingeniously simple hack, and I can't believe no one's thought of it before. Plus, it also works for motion-sensing garage doors and gates that use PIR sensors. You just have to hold the can upside down, and spray the air directly at the sensor. This trick, however, will not work on any type of access-controlled egress doors that are electro-magnetic.

The reason this works is because PIR sensors detect changes in infrared (IR) light radiating in front of them, which is radiant energy that is invisible to the human eye. Anything above absolute zero has an IR signature, including the gas in canned air, which can reach well below-freezing temperatures when the can is turned upside down. This change in IR light can be picked up by the PIR sensor, just like the heat in a human body.

In Samy's next video, he'll explain this more and show off what PIR sensors can detect (like canned air) and what they can't (like smoke), so stay tuned. Also, make sure to subscribe to Applied Hacking on Samy's website, and his YouTube channel, for updates on his latest research.